a. Field of the Invention
The instant invention is directed toward a surgical device incorporating a brush electrode and methods for using the brush electrode for tissue ablation and other forms of electrosurgical treatment. The brush electrode is composed of a plurality of flexible filaments or bristles for applying therapeutic energy to target tissue for the formation of spot or continuous linear lesions, cauterization incision cutting, and desiccation.
b. Background Art
Surgical devices and techniques utilizing electrodes to transfer therapeutic energy to tissue are well know. Electrosurgery allows for the incision, cauterization, fulguration, and desiccation of tissue through the application of high-power, radio frequency (RF) energy to tissue through an electrode. Ablation techniques, whereby the target tissue is necrotized through coagulation, are also performed using surgical devices with electrodes to transfer RF energy to tissue. Many benefits may be gained by forming lesions in tissue—for example, control of cardiac arrhythmia or tachycardia, removal of skin diseases, or the treatment of varicose veins—if the depth and location of the lesions being formed can be controlled. In particular, it can be desirable to elevate tissue temperature to around 50° C. until lesions are formed via coagulation necrosis, which changes the electrical properties of the tissue. For example, when sufficiently deep lesions are formed at specific locations in cardiac tissue via coagulation necrosis, undesirable ventricular tachycardia may be lessened or eliminated. “Sufficiently deep” lesions means transmural lesions in some cardiac applications.
Several difficulties may be encountered, however, when attempting to form adequately-deep lesions at specific locations using some existing surgical ablation electrodes. For example, when forming lesions with RF energy, high temperature gradients are often encountered in the vicinity of the electrode. At the edges of some existing electrodes are regions of very high current density leading to large temperature gradients and hot spots. These “edge effects” may result in the formation of undesirable coagulum and charring of the surface tissue. For example, undesirable coagulum may begin to form when blood reaches around 80° C. for an appreciable length of time, and undesirable tissue charring and desiccation may be seen when tissue reaches around 100° C. for an appreciable length of time. There two types of undesirable coagulum: coagulum that adheres to and damages the medical device; and coagulum blood clots or curds that may enter a patient's bloodstream, possibly resulting in other health problems for the patient. Charring of the surface tissue may also have deleterious effects on a patient.
As the temperature of the electrode is increased, the contact time required to form an adequately-deep lesion decreases, but the likelihood of charring surface tissue and forming undesirable coagulum increases. As the temperature of the electrode is decreased, the contact time required to form an adequately-deep lesion increases, but the likelihood of charring surface tissue and forming undesirable coagulum decreases. It is, therefore, a balancing act trying to ensure that tissue temperatures are adequately high for long enough to create deep lesions, while still preventing or minimizing coagulum formation and/or charring of the surface tissue. Active temperature control may help, but the placement of thermocouples, for example, is tricky and setting the RF generator for a certain temperature becomes an empirical exercise as actual tissue temperatures are generally different from those recorded next to the electrode due to factors such as convection and instrument design.
Another difficulty encountered with existing electrosurgical and ablation electrodes is assurance of adequate tissue contact. Current techniques for creating continuous linear lesions in epicardial or other applications include, for example, dragging a conventional electrode on the tissue, using an array electrode, or using pre-formed electrodes. All of these devices comprise rigid electrodes that do not always conform to the tissue surface, especially when sharp gradients and undulations are present. Consequently, continuous linear lesions are difficult to achieve on trabecular surfaces. When forming lesions on an epicardial surface of a heart, for example, the beating of the heart further complicates matters, making it difficult to keep adequate contact between the electrode and the tissue for a sufficient length of time to form a desired lesion. With a rigid electrode, it can be quite difficult to maintain sufficient contact pressure until an adequate lesion has been formed. This problem is exacerbated on contoured or trabecular surfaces. If the contact between the electrode and the tissue cannot be properly maintained, a quality lesion is unlikely to be formed.
Ablation devices based upon a virtual electrode may address some of the difficulties, but these devices often require high flow rates of conductive fluid (e.g., typically around 70 milliliters per minute) to maintain effective cooling for high-power, RF applications. The introduction of a large amount of conductive fluid into a patient's bloodstream may have detrimental effects on the patient. Concerns also arise when using present electrosurgical devices, which can undesirably char tissue when used for incision and coagulation purposes during surgery.
Thus, there remains a need for a surgical instrument that address these issues with the existing designs and that permits the formation of uniform spot and continuous linear lesions, including transmural lesions, on smooth or contoured surfaces.
The information included in this background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention is to be bound.